Metal turning basically involves rotating a metal workpiece while simultaneously moving a tool holder axially along the workpiece. The tool holder incorporates a cutter that is advanced radially relative to the surface of the workpiece so that a metal chip is continuously formed, which curls away from the workpiece, generally in a tight spiral. The cutter is advanced radially to the greatest degree possible, and the tool holder moved with the greatest axial feed possible, without creating excessive cutting forces. For any given radial advance and axial feed, the chip produced will have a predetermined and relatively constant radial width and axial thickness, both of which are relatively small. The length of the chip, however, will be potentially very great, as there is nothing to break it beyond its own weight, or contact with another object. For maximum efficiency in chip handling, it would be desirable to repeatedly break up the chip as it was formed.
It is known in the art to repeatedly break the chip as it is formed with various apparatuses that vibrate the cutter axially back and forth relative to the tool holder as it moves. Known apparatuses that do this vibrate the cutter continually, creating a sinusoidal pattern relative to the circular surface of the workpiece, and so require that the vibration of the cutter be deliberately kept in an out-of-phase relationship to the rotation of the workpiece. If the two were not kept out-of-phase, the chips would not break up. Instead, long chips would continuously form that also had a wavy shape superimposed upon their length, but which would not break any more readily than a straight chip. There are several examples of patented apparatuses and methods designed to assure the necessary out-of-phase relation.